In recent years, use of renewable energy such as wind and sunlight is actively discussed in view of solving problems related to energy. For example, PTL 1 discloses a vehicle power supply system that uses a solar battery module. The vehicle power supply system supplies power from the solar battery module to a load via a storage battery (secondary battery) and a control circuit. This enables reduction of degradation of fuel efficiency due to supply of power from a generator (alternator) to the load.
Incidentally, auxiliary equipment and electric components of a vehicle are usually driven by power that is accumulated in a lead storage battery. Thus, a capacity of the lead storage battery is set such that the total power consumption of the auxiliary equipment and the electric components does not exceed the power supply capability of the lead storage battery for a long time. Further, the lead storage battery is charged with power generated by the generator (alternator) that is connected with an engine while the engine operates. Thus, a power generation amount of the generator is set not to stay below the total power consumption of the auxiliary equipment and the electric components for a long time. This hinders the power amount (electricity amount) that the lead storage battery is capable of outputting from becoming very low (dead battery).
Recent vehicles in many cases employ a start-stop function that turns off the engine while the vehicle stands still for improving fuel efficiency. In this case, power for driving a starter that restarts the engine is usually supplied from the lead storage battery (for example, PTL 2).